1. Technical Field
The technical field relates to a torque sensing device which detects the strain to obtain the torsion value, and a rotational driving tool integrated with the torque sensing device.
2. Related Art
The traditional rotational driving mechanisms all generate torsion. However, during the process of transferring the torsion, it becomes a problem for how to precisely detect the variation of the torsion value.
The U.S. Pat. Nos. 5,172,774 and 8,302,702, and US Patent Publication Nos. 20100139432 and 20150135856 all disclose using a strain gauge as a sensor to detect the variation of the torsion value which is generated by the torsion driving device.
The conventional strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The pattern is a long, thin conductive strip in a zig-zag pattern of parallel lines. When in use, the strain gauge can be fixed to a metal carrier material which can deform with the strain gauge when receiving load. When the strain gauge deforms with the carrier material under deformation process, the strain of the carrier material can be observed through the variation of the resistance value.
Those patents mentioned above teach using mechanical component as a carrier material to work with strain gauge, and the applied force of the torsion can be absorbed by the carrier material, so as to generate strain to force the strain gauge to deform along with the carrier material, and thus the variation of the torsion in the driving mechanism can be obtained.
However, the position that the strain gauge is installed on the carrier material in the aforementioned patents cannot ideally detect the strain transformed from the torsion. For example, the US Patent Publication No. 5172774 teaches directly installing a plurality of strain gauges on a plurality of shear webs formed by a gear being able to transfer torsion, and the shear webs are used as the carrier material. Even though the shear webs can transfer the loading along the web surface to generate strain, the detected strain not only includes the normal direction strain, but also includes a shear strain, which results in that the strain generated by the shear web cannot fully represent the torsion variation of the gear, and thus the accuracy and precision of the torsion detection cannot be achieved.
Besides, the US Patent Publication No. 20100139432 discloses a transducer fixed to the casing for pivotally connecting to the torque shaft, the transducer is formed as a round plate shape and has a hub for pivotally connecting to the torque shaft. The surrounding of the hub extends to form a disk-shaped web having a ring, and the web is used as the aforementioned carrier material to be installed at least one strain gauge to the variation of the torque shaft. However, the web is formed in disk-shaped ring, which is hard to transfer the applied force transformed from the torsion in a converged way. In other words, the strain generated from the web due to the torsion transfer will be dispersed to the whole area of the ring-shaped web, which can significantly reduce the deformation of the strain gauge, so as to relatively decrease the accuracy and precision of the torsion detection.
Besides, the US Patent Publication No. 8302702 discloses installing the strain gauge to surfaces of side edges of a frame-shaped torque transferring element, and the center of the frame-shaped torque transferring element is connected to an annular gear to use the strain gauge to detect the torsion of the annular gear. However, the side edges of the frame-shaped torque transferring element and the center of the annular gear transfer the action force through the ring-shaped element around the torque transferring element, which force the position where the strain gauge installed suffering bending torque, and thus the precision and accuracy of the torsion detection cannot be achieved.
The US Patent Publication No. 20150135856 discloses a wheel base type force torque sensor for detecting the force or torsion generated when the system meets an obstacle, which is usually used for safety purpose. The center of the force torque sensor also forms a hub coaxially connecting to the rotation element, and the periphery of the force torque sensor is also formed a rim structure. A plurality of beams is formed between the periphery of the hub and the rim, and the end surface of the periphery of the beams can respectively be installed with a strain gauge. The beams are used to transform the received loading to the bending loading to the beam to generate tensile force/compressing force/shear force, so as to allow the strain gauge installed on the beam to detect the strain generated from the beam, and the variation of the torsion value can be observed. However, the aforementioned Patent does not further disclose how the beams transform the received loading to the tensile force/compressing force/shear force, so that the end surface of the periphery of the beams should be installed with strain gauge to increase the accuracy of the detection, which may cause using too many strain gauges and increasing the complexity of the strain structure.
Also, it can be known from the aforementioned techniques that, the traditional torque sensor equipped with strain gauge does not design the position of the beams relative to the torsion center according to the deformation direction of the strain gauge even though the traditional torque sensor uses the tensile strain/compressing strain generated by the beams under loading to force the strain gauge to generate corresponding deformation.